prefer-exponentiation-operator.js

/**
 * @fileoverview Rule to disallow Math.pow in favor of the ** operator
 * @author Milos Djermanovic
 */

"use strict";

//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------

const astUtils = require("./utils/ast-utils");
const { CALL, ReferenceTracker } = require("eslint-utils");

//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------

const PRECEDENCE_OF_EXPONENTIATION_EXPR = astUtils.getPrecedence({ type: "BinaryExpression", operator: "**" });

/**
 * Determines whether the given node needs parens if used as the base in an exponentiation binary expression.
 * @param {ASTNode} base The node to check.
 * @returns {boolean} `true` if the node needs to be parenthesised.
 */
function doesBaseNeedParens(base) {
    return (

        // '**' is right-associative, parens are needed when Math.pow(a ** b, c) is converted to (a ** b) ** c
        astUtils.getPrecedence(base) <= PRECEDENCE_OF_EXPONENTIATION_EXPR ||

        // An unary operator cannot be used immediately before an exponentiation expression
        base.type === "AwaitExpression" ||
        base.type === "UnaryExpression"
    );
}

/**
 * Determines whether the given node needs parens if used as the exponent in an exponentiation binary expression.
 * @param {ASTNode} exponent The node to check.
 * @returns {boolean} `true` if the node needs to be parenthesised.
 */
function doesExponentNeedParens(exponent) {

    // '**' is right-associative, there is no need for parens when Math.pow(a, b ** c) is converted to a ** b ** c
    return astUtils.getPrecedence(exponent) < PRECEDENCE_OF_EXPONENTIATION_EXPR;
}

/**
 * Determines whether an exponentiation binary expression at the place of the given node would need parens.
 * @param {ASTNode} node A node that would be replaced by an exponentiation binary expression.
 * @param {SourceCode} sourceCode A SourceCode object.
 * @returns {boolean} `true` if the expression needs to be parenthesised.
 */
function doesExponentiationExpressionNeedParens(node, sourceCode) {
    const parent = node.parent.type === "ChainExpression" ? node.parent.parent : node.parent;

    const needsParens = (
        parent.type === "ClassDeclaration" ||
        (
            parent.type.endsWith("Expression") &&
            astUtils.getPrecedence(parent) >= PRECEDENCE_OF_EXPONENTIATION_EXPR &&
            !(parent.type === "BinaryExpression" && parent.operator === "**" && parent.right === node) &&
            !((parent.type === "CallExpression" || parent.type === "NewExpression") && parent.arguments.includes(node)) &&
            !(parent.type === "MemberExpression" && parent.computed && parent.property === node) &&
            !(parent.type === "ArrayExpression")
        )
    );

    return needsParens && !astUtils.isParenthesised(sourceCode, node);